"Either stop the war or fund the crisis. Option three is, do both of them."

A Saudi-led coalition embarked on a campaign in March 2015 in Yemen with the aim of dislodging Houthi rebels who control the capital and much of the north and restoring to power the internationally-recognised government of Abd-Rabbu Mansour Hadi.

Since fighting began, more than 10,000 people have been killed, and millions have been driven from their homes.

The country is also facing a health crisis, with more than 2,000 people having died from cholera since April, more than half a million people infected, and another 600,000 expected to contract the infection this year.

The kingdom has said that hundreds of millions of dollars it pledged to humanitarian programmes have benefited civilians on both sides of Yemen's conflict.

Saudi Arabia's Crown Prince Mohammed bin Salman donated $66 million in June to the United Nations Children's Fund and the World Health Organization (WHO) to help combat the cholera epidemic in Yemen.

'Serious complications'

Aid groups have also accused Saudi Arabia of blocking needed assistance and goods from areas that are most in need.

Saudi Arabia and its allies have said they aim to prevent arms shipments to the Houthis, but aid groups say the curbs have deepened the suffering of millions.

Aid agencies have called for greater access to the Houthi-run north, and the UN has accused the coalition of restricting entry to vessels bound for the key Red Sea port of Hodeidah through which around 80 percent of Yemen's food imports once arrived.

"We are having problems with access," the WFP's Beasley said.

"The Saudis have created serious complications for us because of the port being blockaded to a certain degree, and the destroying of the cranes at Hodeidah port ... That has substantially reduced our capacity to bring food in."

Beasley added that coalition restrictions had obstructed the delivery of fuel needed by UN vehicles which travel in and out of Sanaa carrying aid and personnel.